Shallow trench isolation (STI) structure is an important isolation structure for isolating devices in semiconductor device fabrication. A method for forming the shallow trench isolation structure may include providing a semiconductor substrate, forming a shallow trench in the semiconductor substrate, forming an insulating layer on the surface of the semiconductor substrate and in the shallow trench, using a chemical mechanical polishing process to remove the insulating layer on the surface of the semiconductor substrate, and forming a shallow trench isolation structure in the shallow trench.
The device size gets smaller and smaller as the continuous developing of the semiconductor technology. With the reducing of the width of the shallow trench isolation structure, the aspect ratio of the shallow trench for forming the shallow trench isolation structure may be increased continuously. During the process of forming the insulating layer, the insulating material may be accumulated easily along the surface of the sidewalls nearby the top of the shallow trench.
Therefore, a thickness of a portion of the insulating film at the sidewalls of the top of the shallow trench may be larger than a thickness of another portion of the insulating film at the bottom of the shallow trench. When the insulating material is continually to be deposited, the portion of the insulating film on the top of the shallow trench may be closed in advance, which may result in gaps in the formed shallow trench isolation structures.
In order to eliminate the gaps during filling insulating material into a high aspect ratio shallow, a high aspect ratio deposition process (HARP) can be used to form an insulating layer to satisfy the filling requirement of the high aspect ratio shallow trenches. Specifically, tetraethyl orthosilicate (TEOS) and ozone (O3) can be used as reactive gases during the HARP process for filling the high aspect ratio shallow trench.
However, as the aspect ratio of the shallow trench increasing, the performance of the shallow trench isolation structure forming by the existing fabricating process may not be satisfactorily acceptable.